1) This study examined the quality of ventilation delivered during simulated cardiac arrest by 97 healthcare professionals from various specialties using a manikin. 2) The participants hyperventilated the simulated patient, providing a mean minute ventilation of 13.1 L/min compared to guidelines recommending 5 L/min. 3) Suboptimal ventilation exceeding guidelines was found across all specialties, though doctors performed best. The results suggest continued hyperventilation during cardiac arrest contrary to guidelines and research on its adverse effects.